1. Field of the Invention
The present invention relates to field emitter arrays and particularly to a computer memory element based on field emitter arrays.
2. Description of the Prior Art
Computer memory devices are generally based on semiconductor devices where the charge transport is within a solid. There are also electron beam addressable memory devices known in the art. Electron beam devices use macroscopic electron guns to focus a beam of electrons onto specific targets which charge up and retain a static charge. That is, these devices use cathode ray tube or scanning electron microscope technology where the faceplate or target contains all of the memory cells.
The prior art as it relates to this invention is found in the fields of field emitter array devices, semiconductor based computer memory devices, and electron beam addressable memory devices.
The technology of electron beam addressable memory devices essentially directs an electron beam to a target surface where it changes the amount of charge at a specific location. The devices are large, and are made from individual, macro-components, such as cathode ray tube electron guns. These devices require highly regulated power supplies, and the electron beam control electronics is expensive. Furthermore, the memory has to be continuously refreshed. Electron beam devices also suffer from the fact that they are slow in both reading and writing compared to the subject invention.
Semiconductor memories known in the art are also inherently slower than the present invention by several orders of magnitude. Semiconductor devices are also radiation sensitive, and they are strongly effected by both extremely low and extremely high temperatures. For these reasons, they are limited in their application for military hardware, and where temperature and radiation extremes are expected.
Field emitter array devices are well known in the art, as shown in U.S. Pat. No. 4,721,885, entitled "Very High Speed Integrated Microelectronic Tubes"; U.S. Pat. No. 4,578,614, entitled "Ultra-Fast Field Emitter Array Vacuum Integrated Circuit Switching Device"; U.S. Pat. No. 4,513,308, entitled "P-N Junction controlled Field Emitter Array Cathode"; and U.S. Pat. No. 4,307,507, entitled "Method of Manufacturing a Field-Emission Cathode Structure".
U.S. Pat. No. 4,163,949 entitled "Tubistor" discloses a grown oxide-metal composite having at least a million individual emitting points in each square centimeter of material. This patent discusses the analogy between vacuum tube technology and field emitter devices and states that this type of construction can be used to develop a diode, triode, multigrid, or multicathode structure. However, there is no disclosure of multiple anode, single cathode structures, and no electron deflectors are disclosed. There are also no memory concepts or circuits disclosed.
U.S. Pat. No. 4,728,851, entitled "Field Emitter Device with Gated Memory", discloses a field emitter device having a gate electrode adjacent to an emitter electrode for controlling the initial flow of electrons between the cathode and a collector element. This device is a bistable element which may be used with a display where the collector may be coated with a luminescent material. This device uses a gating electrode to establish the flow between the emitter and the anode. Once flow is established, it is maintained even though the voltage to the gate is removed. It is disclosed that the device provides a bistable memory type device. There is no suggestion of circuitry, or any other means, by which a memory element may be controlled and/or switched. Still further, this device cannot be changed from a first conducting state to a second conducting state by means of a control or deflection electrode. The control grid only permits turning on the device, and does not enable the device to be turned off.